Method and apparatus for surface processing of printed wiring board

ABSTRACT

A printed wiring board having a conductor pattern on which a pre-flux film of a stabilized quality is to be formed using a water-soluble pre-flux liquid. To this end, such an apparatus is used which includes an etching unit  12  for etching lands  5   b   , 6   b  formed on the printed wiring board  1 , a rinsing unit  13  for rinsing the printed wiring board  1 , a bubble removing unit  14  for removing air bubbles  58  attached to the printed wiring board  1  on immersing the printed wiring board  1  in a water-soluble pre-flux liquid  9   a  in a processing vessel  56 , a pre-flux forming unit  15  for forming a pre-flux film  9  on the lands  5   b   , 6   b  of the printed wiring board  1  in the pre-flux liquid  9   a  using an in-liquid spraying unit  61 , a liquid removing unit  16  for removing the pre-flux liquid  9   a  from the printed wiring board  1  transported from the processing vessel  56  and a rinsing unit  17  for rinsing the printed wiring board  1.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for a printed wiringboard for forming a protective water-soluble pre-flux film on thesurface of a conductor pattern facing outwards.

2. Description of Related Art

In a printed wiring board, a pre-flux film is routinely formed on itsconductor pattern following the formation of the conductor pattern andprior to ultimate inspection such as substrate appearance inspection.For forming this pre-flux film, a solvent type pre-flux or awater-soluble pre-flux is used.

Meanwhile, since the solvent type pre-flux, which enables qualitystability for the pre-flux film due to its high adhesion to a conductorpattern to assure stabilized film forming and also due to its superiorsolder wettability, is prepared using a large quantity of the volatileorganic compounds (VOCs), the tendency is to use the solvent typepre-flux only in a limited quantity in view of environmental protection.

On the other hand, in a water-soluble pre-flux, not employing the VOCs,sufficient quality stability cannot be realized as compared to thesolvent type pre-flux. For example, the water-soluble pre-flux isinferior to the solvent type pre-flux in adhesion to the conductorpattern, such that stable pre-flux films cannot be formed. In addition,the water-soluble pre-flux liquid is inferior in solder wettability.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand apparatus for surface treatment of a printed wiring board capable offorming a pre-flux film of stable quality on a conductor pattern using awater-soluble pre-flux.

In one aspect, the present invention provides a surface-processingapparatus for a printed wiring board including means for etching thesurface of a conductor pattern formed on at least one surface of aprinted wiring board, first rinsing means for rinsing the surface of theprinted wiring board the conductor pattern of which has been etched bythe etching means, air bubble removing means for removing air bubblesaffixed to the surface of the printed wiring board by immersing theprinted wiring board rinsed by the first rinsing means in awater-soluble pre-flux liquid in a processing vessel, pre-flux formingmeans for forming a pre-flux film on the conductor pattern on theprinted wiring board in the pre-flux liquid, freed of air bubbles by theair bubble removing means, using an in-liquid spray provided in thepre-flux liquid in the processing vessel, liquid removing means forremoving the pre-flux liquid from the surface of the printed wiringboard carrying the pre-flux film and second rinsing means for rinsingthe surface of the printed wiring board from the surface of which thepre-flux liquid has been removed by the liquid removing means.

In another aspect, the present invention provides a surface-processingmethod for a printed wiring board including the steps of etching thesurface of a conductor pattern formed on at least one surface of aprinted wiring board, rinsing the surface of the printed wiring boardthe conductor pattern of which has been etched by the etching step,removing air bubbles affixed to the surface of the printed wiring boardby immersing the printed wiring board rinsed by the first rinsing stepin a water-soluble pre-flux liquid in a processing vessel, forming apre-flux film on the conductor pattern on the printed wiring board inthe pre-flux liquid, freed of air bubbles, using an in-liquid sprayprovided in the pre-flux liquid in the processing vessel, removing thepre-flux liquid from the surface of the printed wiring board carryingthe pre-flux film and transferred from the processing vessel, andrinsing the surface of the printed wiring board from the surface ofwhich the pre-flux liquid has been removed by the liquid removing step.

According to the present invention, the conductor patterns on theprinted wiring board are etched to remove surface oxides to provide fora planar surface. The liquid etchant then is rinsed off to form apre-flux film. So, the pre-flux film may be improved in adhesion, whilethe pre-flux film is not affected by the surface oxides on the conductorpatterns and hence may be a smooth surface. The pre-flux film is formedusing an in-liquid spraying unit, so that it may be of uniform filmthickness, while solder wettability is also improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a printed wiring board.

FIGS. 2A to 2D illustrate the structure of a surface processingapparatus for the printed wiring board shown in FIG. 1.

FIG. 3 illustrates a lower saucer provided below the bubble removingroll.

FIG. 4 illustrates a step for forming a pre-flux film on a land of theprinted wiring board.

FIG. 5 is a cross-sectional view showing essential parts of the printedwiring board showing the state in which crests and recesses are formedby oxidation of a land surface.

FIG. 6 is a cross-sectional view of a printed wiring board the landsurface of which has been flattened out as a result of soft-etching andoxidation of the land surface.

FIG. 7 is a cross-sectional view showing the state of formation of apre-flux film on the land surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, a method and apparatus for surface-processinga printed wiring board for forming a pre-flux film on a land of each ofthe upper and lower surfaces of the printed wiring board carrying pluralconductor patterns according to the present invention will be explainedin detail.

Before proceeding to the description of the surface-processing methodand apparatus, a printed wiring board used therein is explained.Referring to FIG. 1, the printed wiring board 1 includes inner layersubstrates 2, 3. The inner layer substrate 2 includes a conductorpattern 2 a, as a second layer, on its one surface, and a conductorpattern 2 b, as a third layer, on its opposite surface. The inner layersubstrate 3 includes a conductor pattern 3 a, as a fourth layer, on itsone surface, and a conductor pattern 3 b, as a fifth layer, on itsopposite surface. The inner layer substrates 2, 3 are pressed together,with the conductor pattern 2 b as the third layer facing the conductorpattern 3 a as the fourth layer, with the interposition of a pre-preg 4,comprised of glass fibers impregnated with an epoxy resin.

On the inner layer substrate 2 is formed a conductor pattern 5 a, as afirst layer, with the interposition of an outer layer substrate 5 formedof a pre-preg. On the inner layer substrate 3 is formed a conductorpattern 6 a, as a first layer, with the interposition of an outer layersubstrate 6 formed of a pre-preg. The outer layer substrate 5, innerlayer substrate 2, pre-preg 4, inner layer substrate 3 and the outerlayer substrate 6 are layered in this order to form the printed wiringboard 1, through which a via-hole 7 is bored, such as with a drill. Onthe inner wall surface of this via-hole 7, there is formed a platinglayer 7 a, such as with an electrolytic copper plating method or anelectroless copper plating method, to provide for electrical connectionbetween the first layer of the conductor pattern 5 a and the secondlayer of the conductor pattern 2 a, by way of an example. On the outerlayer substrates 5, 6, there are formed solder resists 8, 8, in such amanner that lands 5 b, 6 b, as part of the conductor patterns 5 a, 6 awill face outwards. These lands 5 b, 6 b are used for mountingelectronic components thereon. There are formed protective pre-fluxfilms 9, mainly composed of an imidazole compound, on the lands 5 b, 6b.

For preparing the printed wiring board 1, the conductor patterns 2 a, 2b are formed on both sides of the inner layer substrate 2, whilst theconductor patterns 3 a, 3 b are formed on both sides of the inner layersubstrate 3. The outer layer substrate 5, having a copper foil bonded toits one surface, the inner layer substrate 2 carrying the conductorpatterns 2 a, 2 b, the prepreg 4, the inner layer substrate 3, carryingthe conductor patterns 3 a, 3 b, and the outer layer substrate 6, havinga copper foil bonded to its one surface, are hot-pressed together invacuum to a unified structure. The via-hole 7 then is bored and theplating layer 7 a is formed on the inner wall surface of the via-hole 7,after which conductor patterns 5 a, 6 a are formed on the outer layersubstrates 5 and 6. The solder resists 8, 8 then are applied to theprinted wiring board 1 so that the lands 5 b, 6 b will face outwards.The pre-flux film 9 then is formed on each of the lands 5 b, 6 b bye.g., a surface-processing device.

The surface-processing device 10 for forming the pre-flux film 9surface-processes the lands 5 b, 6 b of the printed wiring board 1 priorto the formation of the pre-flux films 9, that is the printed wiringboard 1 carrying the solder resists 8, 8 on the surfaces of the outerlayer substrates 5, 6. Referring to FIG. 2, the surface-processingdevice 10 includes a rinsing unit 11 for rinsing the printed wiringboard 1, coated with the solder resists 8, 8, and an etching unit 12 foretching the lands 5 b, 6 b, as part of the conductor patterns 5 a, 6 a,facing outwards from the solder resists 8, 8. The surface-processingdevice 10 also includes a rinsing unit 13 for rinsing the printed wiringboard 1, having its lands 5 b, 6 b etched by the etching unit 12, and abubble removing unit 14 for removing the bubbles affixed to the surfaceof the printed wiring board 1 when the printed wiring board 1 rinsed bythe rinsing unit 13 is dipped in a water-soluble pre-flux liquid. Thesurface-processing device 10 also includes a pre-flux forming unit 15for forming pre-flux films 9 on the lands 5 b, 6 b facing outwards fromthe solder resists 8, 8 of the printed wiring board 1, freed of bubblesby the bubble removing unit 14, and a liquid removing unit 16 forremoving the pre-flux liquid from the surface of the printed wiringboard 1 on which the pre-flux film 9 has been formed. Thesurface-processing 10 also includes a rinsing unit 17 for rinsing theprinted wiring board 1 carrying the pre-flux films 9 and freed of theliquid by the liquid removing unit 16, a drying unit 18 for drying theprinted wiring board 1 washed by the rinsing unit 17, and a cooling unit19 for cooling the printed wiring board 1 dried by the drying unit 18.The printed wiring board 1 is continuously transported at a speed of 3m/min in the horizontally laid state, by a transporting unit, in thedirection indicated by arrow A in FIG. 2, through the rinsing unit 11,etching unit 12, rinsing unit 13 bubble removing unit 14, pre-fluxforming unit 15, liquid removing unit 16, rinsing unit 17, drying unit18 and the cooling unit 19, in this order. The rinsing unit 11, to whichis transported the printed wiring board 1, coated with the solderresists 8, 8 and inspected as to the electrical conducting state,includes a transporting unit 21 for transporting the printed wiringboard 1 in the horizontal position, and a spraying unit 22 for sprayingthe rinsing water, as shown in FIG. 2A. The transporting unit 21 is madeup of plural rolls arranged on upper and lower sides of the printedwiring board 1 for holding the printed wiring board 1 transported in thehorizontal position. The transporting unit 21 transports the printedwiring board 1 in the direction indicated by arrow A in FIG. 2A at e.g.,a transporting speed of 3 m/min for positively rinsing the printedwiring board 1. As for the spraying unit 22, two spraying units areprovided on the upper surface side and on the lower surface side of theprinted wiring board 1 transported to the transporting unit 21, sincethe pre-flux films 9 need to be formed on both sides of the printedwiring board 1 and hence the both sides of the printed wiring board 1need to be rinsed. These spraying units 22 spray well water at ambienttemperature under a condition of the spraying pressure not less than 0.1MPa. Thus, the rinsing unit 11 frees the surface of the printed wiringboard 1 of impurities, such as dust and dirt, affixed to the surface ofthe printed wiring board 1.

The etching unit 12, used for etching the lands 5 b, 6 b of the printedwiring board 1, the surfaces of which have been washed by the rinsingunit 11, includes a processing vessel 24 in which to store an liquidetchant 24 a, and a transporting unit 25 for transporting the printedwiring board 1 through the liquid etchant 24 a. The liquid etchant 24 astored in the processing vessel 24 may, for example, be mainly composedof sulfurated water, such as PRT-01 (trade name of a productmanufactured by MECK INC). The transporting unit 25 is made up of pluralrolls arranged on upper and lower surface sides of the printed wiringboard 1 for holding the printed wiring board 1 transported in ahorizontal position. The transporting unit 25 transports the printedwiring board 1 at the same transporting speed of 3 m/min as thetransporting unit 21 of the rinsing unit 11, in the direction indicatedby arrow A in FIG. 2A, in order to positively remove oxides on thesurfaces of the lands 5 b, 6 b by soft etching. The printed wiring board1 is dipped e.g., for 30 seconds in the liquid etchant 24 a at 30° C. sothat the lands 5 b, 6 b as part of the conductor patterns 5 a, 6 a areetched e.g., by 1.5 to 2.5 μm. The soft etching of the lands 5 b, 6 b isrepresented by the following reaction formula:

Cu⁺+H₂O₂+H₂SO₄→CuSO₄+2H₂O.

This removes oxides affixed to the lands 5 b, 6 b formed by theconductor patterns 5 a, 6 a being exposed to outside of the solderresists 8, 8.

Referring to FIGS. 2A and 2B, the rinsing unit 13 for washing theprinted wiring board 1, having its lands 5 b, 6 b etched by the etchingunit 12, includes a water washing unit 27 for washing the printed wiringboard 1, having its lands 5 b, 6 b etched, and an acid washing unit 28for acid-washing the printed wiring board 1 water-washed by the waterwashing unit 27. The rinsing unit 13 also includes a water washing unit29 for water-washing the printed wiring board 1, acid-washed by the acidwashing unit 28, an intermediate pressure water washing unit 30 forwater-washing the printed wiring board 1 at a higher pressure than inthe water washing unit 29, and an abundant water washing unit 31 forwashing the printed wiring board 1 with an abundant flow of rinsingwater. The rinsing unit 13 also includes a second water washing unit 32for further water-washing the printed wiring board 1 from the abundantwater washing unit 31 and an air blower unit 33 for removing themoisture affixed to the surface o the printed wiring board 1.

Referring to FIG. 2A, the water washing unit 27 for water-washing theprinted wiring board 1, having the lands 5 b, 6 b etched by the etchingunit 12, includes a transporting unit 35 for transporting the printedwiring board 1 in the horizontal state, and a spraying unit 36 forejecting rinsing water. A plurality of transporting units 35 arearranged on the upper and lower surface sides of the printed wiringboard 1. The transporting unit 35 transports the printed wiring board 1in the direction indicated by arrow A in FIG. 2A at a transporting speedof, for example, 3 m/min, in order to remove the liquid etchant 24 aaffixed to the surface of the printed wiring board 1 with the rinsingwater ejected from the spraying unit 36. As for the spraying unit 36,three spraying units each are provided on the upper and lower surfacesides of the printed wiring board 1, transferred by the transportingunit 35, in order to remove the liquid etchant 24 a affixed to bothsurfaces of the printed wiring board 1. These spraying units 36 spraywell water at ambient temperature under a spray pressure of 0.1 MPa orhigher. This enables the water washing unit 27 to free the surface ofthe printed wiring board 1 of the liquid etchant 24 a.

The acid washing unit 28 for acid-washing the printed wiring board 1,freed of the liquid etchant 24 a by the water washing unit 27, includesa transporting unit 38 for transporting the printed wiring board 1 inthe horizontal position and a spraying unit 39 for ejecting sulfuratedwater. As for the transporting unit 38, a plurality of transportingunits 38 are provided on the upper and lower surface sides of theprinted wiring board 1 for clamping the printed wiring board 1transported in the horizontal position. The transporting units 38transfer the printed wiring board 1 in the direction indicated by arrowA in FIG. 2A, at a transfer speed of e.g., 3 m/min, in order topositively remove the oxides from the lands 5 b, 6 b of the printedwiring board 1. As for the spraying units 39, there are provided eachfour spraying units 39 on the upper and lower surface sides of theprinted wiring board 1, being transferred by the transporting unit 35,for positively forming the pre-flux films 9 on the surfaces of the lands5 b, 6 b. These spraying units 39 spray the 5% sulfuric acid sulfuratedwater at room temperature under a spraying pressure not lower than 0.2MPa. This enables the acid washing unit 28 to positively remove theoxides of the lands 5 b, 6 b as part of the surface of the printedwiring board 1. That is, the oxides on the lands 5 b, 6 b are removedpositively by being etched by the etching unit 12 and acid-washed by theacid washing unit 28, as shown in FIGS. 5 and 6.

Meanwhile, the sulfurated water is used for removing oxides on thesurfaces of the conductor patterns 5 a, 6 a, as described above, sothat, if this sulfurated water is left in the via-hole 7 of the printedwiring board 1, there is a risk that the plating layer 7 a formed in thevia-hole 7 be oxidized and ruptured. So, the rinsing unit 13 is designedso that, before forming the pre-flux film 9, the sulfurated water willbe removed positively by the water washing unit 29, intermediatepressure water washing unit 30, abundant water washing unit 31 and thewater washing unit 32.

The water washing unit 29 for water-washing the printed wiring board 1washed with acid by the acid washing unit 28 includes a transportingunit 41 for transferring the printed wiring board 1 in the horizontalstate, and a spraying unit 42 for spraying the rinsing water. As for thetransporting unit 41, plural transporting units 41 are provided on theupper and lower surface sides of the printed wiring board 1. Thetransporting unit 41 transfers the printed wiring board 1 at e.g., atransfer speed of 3 m/min in the direction indicated by arrow A in FIG.2A for positively rinsing the printed wiring board 1. Since the pre-fluxfilms 9 are formed on the lands 5 b, 6 b provided on both sides of theprinted wiring board 1, two each of the spraying units 42 are providedon the upper and lower surface sides of the printed wiring board 1transferred by the transporting unit 41. These spraying units 43 spraypure water at 35° C. under a condition of the spraying pressure not lessthan 0.1 MPa. The pure water at 35° C. is used for improving the waterwashing effect. If the water temperature is not lower than 35° C., thesurfaces of the conductor patterns 5 a, 6 a tend to be oxidized. So, forwashing the printed wiring board 1 until formation of the pre-flux film9, that is washing by the intermediate pressure water washing unit 30,abundant water washing unit 31 and the water washing unit 32, pure waterat 35° C. is used. Thus, the water washing unit 29 removes thesulfurated water from the surface of the printed wiring board 1.

The intermediate pressure water washing unit 30 for further washing theprinted wiring board 1 rinsed with water by the water washing unit 29includes a transporting unit 44 for transferring the printed wiringboard 1 in the horizontal position and a spraying unit 45 for ejectingrinsing water. As for the transporting unit 44, plural transportingunits 44 are provided on the upper and lower surface sides of theprinted wiring board 1 for holding the printed wiring board 1transferred in the horizontal position. The transporting unit 44transfer the printed wiring board 1 at e.g., a transfer speed of 3 m/minin the direction indicated by arrow A in FIG. 2B to enable thesulfurated water to be rinsed off from the printed wiring board 1. Forrinsing the sulfurated water off from the printed wiring board 1, fourspraying units 45 are provided on the upper and lower sides of theprinted wiring board 1 transferred by the transporting unit 44. Thespraying units 45 spray pure water at 35° C. at a pressure higher thanthat used for the water washing unit 29, for example, at a sprayingpressure not lower than 0.5 MPa. This allows the intermediate pressurewater washing unit 30 to remove sulfurated water from the surface of theprinted wiring board 1.

The abundant water washing unit 31 for further washing the printedwiring board 1, water-washed by the intermediate pressure water washingunit 30, includes a transporting unit 47 for transferring the printedwiring board 1 in the horizontal state and a spraying unit 48 forejecting rinsing water. A plurality of transporting units 47 areprovided on the upper and lower sides of the printed wiring board 1transferred by the transporting unit 44. The transporting unit 47transfers the printed wiring board 1 in the direction indicated by arrowA in FIG. 2B, at a transfer rate of e.g., 3 m/min, to enable the rinsingof the printed wiring board 1. Two each of the spraying units 48 areprovided on the upper and lower sides of the printed wiring board 1,transferred by the transporting unit 47, in order to positively rinsesulfurated water off from both sides of the printed wiring board 1.These spraying units 45 spray pure water at 35° C. with a higher waterflow rate than the spraying unit 42 of the water washing unit 29, forexample, at a water flow rate not less than 5 liters/cm². This allowsthe abundant water washing unit 31 to rinse the sulfurated water offfrom the surface of the printed wiring board 1.

The water washing unit 32 for further washing the printed wiring board lwater-washed by the abundant water washing unit 31 includes atransporting unit 50 for transferring the printed wiring board 1 in thehorizontal position, and a spraying unit 51 for ejecting the rinsingwater. A plurality of the transporting units 50 are provided on theupper and lower sides of the printed wiring board 1 for holding theprinted wiring board 1 transferred in the horizontal position. Two eachof the spraying units 51 are provided on the upper and lower sides ofthe printed wiring board 1, transferred by the transporting unit 50, inorder to positively rinse sulfurated water off from both sides of theprinted wiring board 1. These spraying units 51 spray fresh water at aspray pressure not lower than 0.1 MPa. This allows the water washingunit 29 to remove sulfurated water off from the surface of the printedwiring board 1. Here, new pure water, that is fresh water, is used asrinsing water. Thus, the water washing unit 32 is able to prevent theprocessing liquid affixed to the printed wiring board 1, that issulfurated water, from being carried to the next step.

The air blower unit 33 for removing water affixed to the surface of theprinted wiring board 1, washed with water by the water washing unit 32,includes a transporting unit 53 for transferring the printed wiringboard 1 in the horizontal position, and an air ejection unit 54 forejecting air to the upper and lower sides of the printed wiring board 1.A plurality of the transporting units 53 are provided on the upper andlower sides of the printed wiring board 1 for holding the printed wiringboard 1 transferred in the horizontal position. The transporting unit 53transfers the printed wiring board 1 at a transfer rate e.g., of 3 m/minin the direction indicated by arrow A in FIG. 2B in order to positivelyremove the moisture affixed to the the upper and lower sides of theprinted wiring board 1. The air ejection unit 54 is provided on each ofthe upper and lower sides of the printed wiring board 1 to eject air tothe upper and lower sides of the printed wiring board 1 transferred bythe transporting unit 53 to remove the moisture affixed to the printedwiring board 1. The air blower unit 33 is able to remove the moisturepositively from the the upper and lower sides of the printed wiringboard 1 prior to formation of the pre-flux film 9.

The printed wiring board 1, positively freed of surface oxides from thelands 5 b, 6 b by the etching unit 12 and the acid washing unit 28, iswashed with water in four stages of different conditions using the waterwashing unit 29, intermediate pressure water washing mechanism 30,abundant water washing unit 31 and the second water washing unit 32, sothat sulfurated water remaining on the surface and especially in thevia-hole 7 may be removed reliably. Moreover, the intermediate pressurewater washing unit 30 ejects pure water on the upper and lower sides ofthe printed wiring board 1 under a pressure higher than in the ordinarywater washing unit 27 or 29, while the abundant water washing unit 31ejects pure water at a water flow rate higher than in the ordinary waterwashing unit 27 or 29, so that sulfurated water can be removed reliablyfrom the printed wiring board 1. In addition, in the rinsing with purewater, pure water at the water temperature of 35° C. is used to improvethe water washing effect, while it is possible to prevent oxidation ofthe surface of the lands 5 b, 6 b. Thus, with the printed wiring board1, it is possible to prevent sulfurated water from being left on thelands 5 b, 6 b to prevent the lands 5 b, 6 b from being oxidized androughed, while it is also possible to prevent the plating layer 7 aprovided in the via-hole 7 from being oxidized and ruptured.

For forming the pre-flux film 9 on the lands 5 b, 6 b of the printedwiring board 1, freed of surface water by the air blower unit 33, theprinted wiring board 1 is immersed in the pre-flux liquid 9 a stored ina processing vessel 56, as shown in FIG. 2C. The printed wiring board 1is transferred to the bubble removing unit 14 and to the pre-fluxforming unit 15.

This bubble removing unit 14 removes air bubbles 58 generated on thesurface of the printed wiring board 1 when the printed wiring board 1 isimmersed in the pre-flux liquid 9 a of the processing vessel 56, andincludes a processing vessel 56 in which to store the pre-flux liquid 9a and a bubble removing roll 57 operating as a unit for transferring theprinted wiring board 1 in the horizontal position through the pre-fluxliquid 9 a and also for removing air bubbles 58 generated on the surfaceof the printed wiring board 1 when the printed wiring board 1s immersedin the pre-flux liquid 9 a. The pre-flux liquid 9 a, stored in theprocessing vessel 56, is the water-soluble type pre-flux mainly composedof acetic acid and imidazole, such as a pre-flux manufactured by SHIKOKUKASEI CO. LTD. under the trade name of TERFACE F2.

A plurality of bubble removing rolls 57 are provided on the upper andlower sides of the printed wiring board 1 for holding the printed wiringboard 1 transferred in the horizontal position. The bubble removing roll57 transfers the printed wiring board 1 in the direction indicated byarrow A in FIG. 2C at the same transfer speed of 3 m/min as that of theother transporting units 21, 25, 38, 41, 44, 47, 50 and 53. These bubbleremoving rolls 57 are formed like sponge rolls from e.g.,chlorosulfonated polyethylene. The bubble removing roll 57, contactingthe printed wiring board 1, is run in rotation to remove air bubblesaffixed to the surface of the printed wiring board 1 and is able to formthe pre-flux film 9 to a uniform thickness on the lands 5 b, 6 b at thenext step.

The pre-flux forming unit 15 for forming the pre-flux film 9 on thelands 5 b, 6 b of the printed wiring board 1, immersed in the pre-fluxliquid 9 a and freed of surface air bubbles 58 by the bubble removingunit 14, includes a processing vessel 56 in which to store the pre-fluxliquid 9 a, a transporting unit 60 for transferring the printed wiringboard 1 transferred in the horizontal position through the pre-fluxliquid 9 a and an in-liquid spraying unit 61 for spraying the pre-fluxliquid 9 a, as shown in FIG. 2C.

The transporting unit 60 is made up of plural rolls arranged on theupper and lower sides of the printed wiring board 1 for holding theprinted wiring board 1 transferred in the horizontal position. The rollsprovided the upper and lower sides of the printed wiring board 1 arearranged with a gap C larger than the thickness t of the printed wiringboard 1, in-between, and are designed such that the roll pressureapplied to the printed wiring board 1 is decreased and such that no rollmarks will be left on the pre-flux film 9 during its formation to enablethe pre-flux film 9 to be formed to a uniform thickness. For example,the gap C is set to 0.5 mm or less, preferably to 2 mm. The transportingunit 60 transfers the printed wiring board 1 in the direction indicatedby arrow A in FIG. 2C, at a transfer rate e.g., of 3 m/min, as theprinted wiring board 1 is immersed in the water-soluble type pre-fluxliquid 9 a. The printed wiring board 1 is immersed for e.g., 120 secondsin the water-soluble type pre-flux liquid 9 a in the processing vessel56.

For forming the pre-flux film 9 of a uniform film thickness on each ofthe surfaces of the printed wiring board 1, 10 each of in-liquidspraying units 61 are provided on the upper and lower sides of theprinted wiring board 1 transferred by the transporting unit 60. Thesein-liquid spraying units 61 are comprised of flat nozzles and are of theradiating angle of approximately 90° to permit the water-solublepre-flux liquid 9 a to be ejected over a wide range. These in-liquidspraying units 61 spray the water-soluble pre-flux liquid 9 a of 35° C.onto the the upper and lower sides of the printed wiring board 1 under aspraying pressure not less than 0.1 MPa. Since the pre-flux liquid 9 ais ejected onto the printed wiring board 1 by the in-liquid sprayingunits 61 in the pre-flux liquid 9 a, the pre-flux film 9 of a uniformfilm thickness of 0.2 to 0.3 μm is formed on the lands 5 b, 6 b. Thepre-flux film 9, formed on the lands 5 b, 6 b formed by copper foils, ismainly composed of an imidazole compound, and is formed in accordancewith the chemical formula 1:

In the previous process, the lands 5 b, 6 b are soft-etched by theetching unit 12 and further acid-washed by the acid washing unit 28 toremove the surface oxides and to rinse sulfurated water off positivelyand hence are of flat surfaces. Thus, the pre-flux film 9 adheres to thelands 5 b, 6 b intimately and is moreover of a flat surface. So, thepre-flux film 9 adherers positively to the lands 5 b, 6 b and issuperior in solder wetting properties.

When the pre-flux film 9 has been formed by the lands 5 b, 6 b by thepre-flux forming unit 15, the printed wiring board 1 is taken out fromthe processing vessel 56. The printed wiring board 1, taken out from theprocessing vessel 56, is transferred to the liquid removing unit 16 toremove the liquid attached to its surface. This liquid removing unit 16serves as a transfer unit for transferring the printed wiring board 1taken out from the processing vessel 56 in the horizontal position, andincludes upper and lower liquid removing rolls 62 for removing theliquid attached to its surface, and a lower saucer 63 arranged below thelower liquid removing roll 62, as shown in FIGS. 2C and 3.

A plurality of the liquid removing rolls 62 are provided on the upperand lower sides of the printed wiring board 1 for holding the printedwiring board 1 transferred in the horizontal position. The liquidremoving rolls 62 transfer the printed wiring board 1 in the directionindicated by arrow A in FIGS. 2C and 3 at the same transfer rate e.g.,of 3 m/min as that of the other transporting units 21, 25, 38, 41, 44,47, 50, 53, 57 and 60. The liquid removing rolls 62 are formed aswater-absorbent sponge rolls from e.g., chlorosulfonated polyethyleneand is designed to apply its own gravity to the printed wiring board 1.

On the lower side of the printed wiring board 1, transferred by theliquid removing rolls 62, there is provided the lower saucer 63 of e.g.,vinyl chloride for holding substantially the lower half of the liquidremoving rolls 62. Within this lower saucer 63, which is a storage partfor the pre-flux liquid 9 a, the water-soluble pre-flux liquid 9 a iscirculated at a rate of 5 to 10 liters/min. This permits the liquidremoving rolls 62 to be immersed at all times in the new water-solublepre-flux liquid 9 a to prevent the liquid immersing the liquid removingrolls 62 from being oxidized to exfoliate the pre-flux liquid 9 a.

The aforementioned liquid removing unit 16 is able to form the surfaceof the pre-flux film 9 to a flat shape by the sponge-like liquidremoving rolls 62 removing the excess pre-flux liquid 9 a affixed to thesurface of the printed wiring board 1 when the printed wiring board 1 istaken out of the processing vessel 56. In particular, the lower liquidremoving roll 62 is sponge-like and is partially covered by the lowersaucer 63 in which is circulated the pre-flux liquid 9 a. So, the liquidcomponewnt, in which is immersed the liquid removing rolls 62, may beprevented from being oxidized to prevent exfoliation of the pre-fluxfilm 9.

The rinsing unit 17 for rinsing the printed wiring board 1, freed of thesurface pre-flux liquid 9 a by the liquid removing unit 16 and forrinsing the printed wiring board 1 carrying the pre-flux film 9,includes a water washing unit 66 for washing the printed wiring board 1carrying the pre-flux film 9 , a water washing unit 67 for furtherwater-washing the printed wiring board 1 washed with water by the waterwashing unit 66, and an air blower unit 68 for removing the moistureaffixed to the surface of the printed wiring board 1, as shown in FIG.2D.

The rinsing unit 66 for washing the printed wiring board 1, carrying thepre-flux film 9, includes a transporting unit 71 for transferring theprinted wiring board 1 transferred in the horizontal position, and aspraying unit 72 for ejecting the rinsing water, as shown in FIG. 2D. Aplurality of the transporting unit 71 are arranged on the upper andlower sides of the printed wiring board 1 for holding the printed wiringboard 1 transferred in the horizontal position. The transporting unit 71transfers the printed wiring board 1 at a transfer rate e.g., of 3 m/minin the direction indicated by arrow A in FIG. 2D for removing unneededpre-flux liquid 9 a affixed to the surface of the printed wiring board 1and which has not been removed by the liquid removing unit 16. Three ofthe spraying units 72 are provided on the upper and lower sides of theprinted wiring board 1, transferred by the transporting unit 71, forremoving the pre-flux liquid 9 a affixed to the surface of the printedwiring board 1. These spraying units 72 spray new water, that is freshpure water, at ambient temperature, under a spraying pressure not lessthan 0.1 MPa. This pennits the water washing unit 66 to remove thepre-flux liquid 9 a from the surface of the printed wiring board 1. Onthe other hand, by using fresh water, the pre-flux liquid 9 a may beprevented from being carried to the next process step.

The second water washing unit 67 for further water-washing the printedwiring board 1, water-washed by the water washing unit 66, includes atransporting unit 74 for transferring the printed wiring board 1transferred in the horizontal position and a spraying unit 75 forejecting the rinsing water. A plurality of the transporting unit 74 areprovided on the upper and lower sides of the printed wiring board 1 forholding the printed wiring board 1 transferred in the horizontalposition. The transporting unit 74 transfers the printed wiring board 1at a transfer rate e.g., of 3 m/min in the direction indicated by arrowA in FIG. 2D for removing unneeded pre-flux liquid 9 a affixed to thesurface of the printed wiring board 1 and which has not been removed bythe liquid removing unit 66. Two each of the spraying units 75 areprovided on the upper and lower sides of the printed wiring board 1,transferred by the transporting unit 74, for removing the pre-fluxliquid 9 a affixed to the surface of the printed wiring board 1. Thesespraying units 72 spray new water at ambient temperature, under aspraying pressure not less than 0.1 MPa, that is, the water washing unit67 uses the new rinsing water, that is fresh water, without using therinsing water used in the water washing unit 66, for preventing theprocessing liquid, that is the pre-flux liquid 9 a, from being carriedinto the water washing unit 67 to make the rinsing water acidic to peeloff the pre-flux film 9. This permits the water washing unit 67 toremove the pre-flux liquid 9 a positively from the surface of theprinted wiring board 1.

The air blower unit 68 for removing the moisture affixed to the surfaceof the printed wiring board 1, washed with water by the water washingunit 67, includes a transporting mechanism 77 for transferring theprinted wiring board 1 in the horizontal position, and air blowers 78for ejecting air onto the upper and lower sides of the printed wiringboard 1. A plurality of the transporting units 77 are provided on theupper and lower sides of the printed wiring board 1 for holding theprinted wiring board 1 transferred in the horizontal position. Thetransporting unit 77 transfers the printed wiring board 1 in thedirection indicated by arrow A in FIG. 2D at a transfer rate e.g., of 3m/min in order to positively remove the moisture affixed to the printedwiring board 1. The air blowers 78 are provided on the upper and lowersides of the printed wiring board 1 for positively ejecting air onto theupper and lower sides of the printed wiring board 1 of the printedwiring board 1 transferred by the transporting unit 77. The air blowerunit 68 is able to remove the moisture positively from the upper andlower sides of the printed wiring board 1 carrying the pre-flux film 9.

The drier unit 18 for drying the printed wiring board 1, completelyfreed of the unneeded pre-flux liquid by water washing, includes atransporting unit 81 for transferring the printed wiring board 1 in thehorizontal position and a heater 82 for heating the the upper and lowersides of the printed wiring board 1. A plurality of the transportingunits 81 are provided on the upper and lower sides of the printed wiringboard 1. The transporting unit 81 transfers the printed wiring board 1in the direction indicated by arrow A in FIG. 2D at a transfer ratee.g., of 3 m/min for positively removing the moisture affixed to theprinted wiring board 1. The heater 82 heats the inside of a processingchamber to approximately 150° C. The printed wiring board 1, transferredby the transporting unit 81, is positively dried by heating forapproximately 30 seconds.

The cooling unit 19 for cooling the printed wiring board 1 from thedrying unit 18 includes a transporting unit 84 for transferring theprinted wiring board 1 in the horizontal position. A plurality oftransporting units 84 are mounted on the upper and lower sides of theprinted wiring board 1 for holding the printed wiring board 1transferred in the horizontal position. The transporting unit 84 coolsthe printed wiring board 1 at ambient temperature for approximately 20seconds at a transfer rate e.g., of 3 m/min.

The method for forming the pre-flux film 9 on the lands 5 b, 6 b usingthe surface-processing device 10 constructed as described above is nowexplained by referring to FIGS. 2A to 2D.

First, at step S1,the printed wiring board 1, coated with the solderresists 8, 8 and tested for current conduction, is transferred by atransporting unit, not shown, to the rinsing unit 11. The printed wiringboard 1 is transferred by a transporting unit 21 at a transfer ratee.g., of 3 m/min and rinsed as the well water at ambient temperature issprayed thereon under a spraying pressure not less than 0.1 MPa by eachtwo spraying units 22 provided on the upper and lower sides of theprinted wiring board 1. This removes foreign matter, such as dust anddirt, deposited on the surface of the printed wiring board 1 prior toformation of the pre-flux film 9. The printed wiring board 1 thus rinsedis transferred from the transporting unit 21 to the transporting unit 25of the etching unit 12.

Meanwhile, the lands 5 b, 6 b present irregularities due to surfaceoxidation, as shown in FIG. 5. If the pre-flux film 9 is formed on thelands 5 b, 6 b in a state shown in FIG. 5, the pre-flux film 9 isinferior in adhesion to the lands 5 b, 6 b. Moreover, the irregularitieson the lands 5 b, 6 b affect the pre-flux film 9 such that the surfaceof the pre-flux film 9 is also indented to worsen solder wettability.So, the lands 5 b, 6 b are planarized by acid-washing their surfaces bysoft etching to remove surface irregularities, that is oxides.

That is, the lands 5 b, 6 b of the printed wiring board 1, having theirsurfaces washed, are soft-etched at step S2 by the etching unit 12.Specifically, the printed wiring board 1 is transferred at a transferrate e.g., of 3 m/min through the liquid etchant 24 a in the processingvessel 24, mainly composed of sulfurated water, whereby the copper foilsmaking up the lands 5 b, 6 b are etched by 1.5 to 2.5 μm in 30 seconds.This removes the oxides affixed to the lands 5 b, 6 b. The printedwiring board 1, the lands 5 b, 6 b of which have been soft-etched, istransferred from the transporting unit 25 to a transporting unit 35 ofthe water washing unit 27.

The printed wiring board 1, the lands 5 b, 6 b of which have been etchedby the etching unit 12, is freed at step S3 of the liquid etchant 24 aaffixed to the entire surface of the printed wiring board 1 by the waterwashing unit 27. That is, as the printed wiring board 1 is transferredby the transporting unit 35 at a transfer rate e.g., of 3 m/min, wellwater at ambient temperature is sprayed under a spraying pressure notless than 0.1 MPa by each three spraying units 36 provided the upper andlower sides of the printed wiring board 1, whereby the excess liquidetchant 24 a affixed to the surface of the printed wiring board 1 isremoved. The printed wiring board 1, rinsed by the water washing unit27, is transferred from the transporting unit 35 to a transporting unit38 of the acid washing unit 28.

The printed wiring board 1, freed of the liquid etchant 24 a by waterwashing by the water washing unit 27, is freed at step S4 of oxides onthe lands 5 b, 6 b by the acid washing unit 28. Specifically, as theprinted wiring board 1 is transferred at a transfer rate e.g., of 3m/min by the transporting unit 38, 5% sulfuric acid sulfurated water atambient temperature is sprayed on the upper and lower sides of theprinted wiring board 1 under a spraying pressure not less than 0.2 MPaby each four spraying units 39 provided on the upper and lower sides ofthe printed wiring board 1, whereby the oxides of the lands 5 b, 6 b maybe removed positively.

That is, the surfaces of the lands 5 b, 6 b are soft-etched at step S2by the etching unit 12 and acid-washed at step S4 by the acid washingunit 28. That is, the two-stage oxide removing process positivelyremoves the oxides to planarize the surface of the lands 5 b, 6 b. Thisimproves adhesion of the pre-flux film 9 to the lands 5 b, 6 b, whilealso improving solder wettability.

Meanwhile, the sulfurated water is used for removing surface oxides onthe lands 5 b, 6 b, as described above, so that, if this sulfuratedwater is left in the via-hole 7 of the printed wiring board 1, theplating layer 7 a provided in the via-hole 7 tends to be oxidized andruptured. So, at step S5, the printed wiring board 1, the lands 5 b, 6 bof which have been acid-washed by the acid washing unit 28 and which hasbeen transferred by the transporting unit 38, is water-washed by thewater washing unit 38. That is, as the printed wiring board 1 istransferred at a transfer rate e.g., of 3 m/min by the transporting unit41, pure water at 35° C. is ejected under a spraying pressure not lessthan 0.1 MPa by each two spraying units 42 provided on the upper andlower sides of the printed wiring board 1. This rinses sulfurated wateroff from the printed wiring board 1. The printed wiring board 1, washedwith water by the water washing unit 29, is transferred from thetransporting unit 38 to a transporting unit 44 of the intermediatepressure water washing unit 30.

The printed wiring board 1, water-washed at step S6 by the water washingunit 29, is water-washed at a high ejection pressure by the sprayingunits 42 of the water washing unit 29 of the intermediate pressure waterwashing unit 30. Specifically, the printed wiring board 1 is transferredby the transporting unit 44 at a transfer rate e.g., of 3 m/min and hasits upper and lower surfaces sprayed with pure water at 35° C. under aspraying pressure not less than 0.5 MPa by each four spraying units 45provided on the upper and lower sides of the printed wiring board 1.This rinses the sulfurated water off from the printed wiring board 1.The printed wiring board, washed with water by the intermediate pressurewater washing unit 30, is transferred from the transporting unit 44 tothe transporting unit 47 of the abundant water washing unit 31.

The printed wiring board 1, washed with water by the intermediatepressure water washing mechanism 30, is washed at step S7 with anabundant flow of water by the spraying units 42 of the water washingunit 29 of the abundant water washing unit 31. Specifically, the printedwiring board 1 is transferred by the transporting unit 47 at a transferrate e.g., of 3 m/min and sprayed with 35° C. pure water at a flow ratenot less than 5 lit/cm² by each two spraying units provided on the upperand lower sides of the printed wiring board 1. This rinses sulfuratedwater off from the printed wiring board 1. The printed wiring board 1,washed with water by the abundant water washing unit 31, is transferredfrom the transporting unit 47 to the transporting unit 50 of theabundant water washing unit 32.

Att the next step S8, the printed wiring board 1, washed with water bythe abundant water washing unit 31, is washed with new water by thewater washing unit 32. That is, as the printed wiring board 1 istransferred by the transporting unit 50 at a transfer rate e.g., of 3m/min, it is sprayed with fresh water at 35° C. under a sprayingpressure not less than 0.1 MPa by each two spraying units 51 providedthe upper and lower sides of the printed wiring board 1. This completelyrises sulfurated water off from the printed wiring board 1. Here, newpure water, that is fresh water, is used as the rinsing water, toprevent the processing liquid, that is sulfurated water, affixed to theprinted wiring board 1, from being carried to the following processstep. The printed wiring board 1, washed with water by the water washingunit 32, is transported from the transporting unit 50 to thetransporting unit 53 of the air blower unit 33.

The printed wiring board 1, washed with fresh water by the water washingunit 32, is freed at step S9 of water affixed to its surface by the airblower unit 33. Specifically, as the printed wiring board 1 istransferred by the transporting unit 53 at a transfer rate e.g., of 3m/min, air is ejected from an air blower 54 onto the upper and lowersides of the printed wiring board 1 to remove the moisture positivelyfrom the upper and lower sides of the printed wiring board 1 immediatelybefore formation of the pre-flux film 9.

By the four stages of water washing under different conditions employingthe water washing unit 29, intermediate pressure water washing unit 30,abundant water washing unit 31 and the second water washing unit 32 atsteps S5 to S8, the sulfurated water left on the surface of the printedwiring board 1, especially in the via-hole 7, may be removed positively.Moreover, in the rinsing at the steps S5 to S8 employing pure water at35° C., the water-washing effect may be improved, whilst surfaceoxidation of the lands 5 b, 6 b may be prevented from occurring. Byusing fresh water as the rinsing water at step S8, the processing liquidaffixed to the printed wiring board 1, that is sulfurated water, may beprevented from being transferred to the next step.

Thus, with the printed wiring board 1, it is possible to prevent thelands 5 b, 6 b, planarized by soft etching at step S2 and acid washingat step S4, from being oxidized and being again hardened in its surfaceby the sulfurated water left on the lands 5 b, 6 b. Moreover, with theprinted wiring board 1, it is possible to prevent the plating layer 7 ain the via-hole 7 from being oxidized and ruptured. On the lands 5 b, 6b, thus planarized, there is then formed the pre-flux film 9.

That is, the printed wiring board 1, freed of redundant water by the airblower unit 33, is transported from the transporting unit 53 of the airblower unit 33 to a transporting unit, comprised of the bubble removingrolls 57 of the bubble removing unit 14, so as to be immersed in thepre-flux liquid 9 a stored in the processing vessel 56. At this time,air bubbles 58 are generated on the surface of the printed wiring board1. If the pre-flux film 9 is formed as the air bubbles 58 are generatedin this manner, the pre-flux film 9 cannot be formed to a uniform filmthickness. So, the printed wiring board 1, on the surface of which areattached the air bubbles 58, is transferred at a transfer rate e.g., of3 m/min by the bubble removing rolls 57 provided on the upper and lowersides of the printed wiring board 1 for removing the air bubbles 58. Theprinted wiring board 1, freed of the air bubbles 58 on immersion in thepre-flux liquid 9 a in the processing vessel 56, is transferred from thetransporting unit comprised of the bubble removing rolls 57 to thetransporting unit 60 of the pre-flux forming unit 15.

On the lands 5 b, 6 b of the printed wiring board 1, from the surface ofwhich the air bubbles 58 have been removed , the pre-flux film 9 isformed at step S11 by the pre-flux forming unit 15. Specifically, as theprinted wiring board 1 is transferred by the transporting unit 60 at atransfer rate e.g., of 3 m/min through the water-soluble pre-flux liquid9 a in the processing vessel 56, mainly composed of acetic acid andimidazole on the surface of the printed wiring board 1 in the pre-fluxliquid 9 a, the water-soluble pre-flux liquid at 35° C. is sprayed undera spraying pressure not less than 0.1 MPa by each ten in-liquid sprayingunits 61 provided on the upper and lower sides of the printed wiringboard 1. This forms the pre-flux film 9, mainly composed of theimidazole compound, to a uniform film thickness of 0.2 to 0.3 μm, on thelands 5 b, 6 b. Since these lands 5 b, 6 b are formed to flat surfacesby soft etching at step S2 and by acid washing at step S4, as previoussteps, as shown in FIG. 7, the pre-flux film 9 is intimately affixed tothe lands 5 b, 6 b and formed to a planar surface. This enables thepre-flux film 9 to be generated with high adhesion properties withrespect to the lands 5 b, 6 b and excellent solder wettability. Theupper and lower paired rolls, making up the transporting unit 60, arearranged at the intervals larger than the thickness of the printedwiring board 1. So, the roll pressure applied to the surface of theprinted wiring board 1 is reduced to prevent roll marks from being lefton the surface of the pre-flux film 9 being formed to rough the surface.The printed wiring board 1, now carrying the pre-flux film 9 on itslands 5 b, 6 b, is transferred from the transporting unit 60 to theliquid removing unit 16. Meanwhile, the printed wiring board 1 isimmersed for 120 seconds in the pre-flux liquid 9 a in the processingvessel 56.

At step S12, the printed wiring board 1, now carrying the pre-flux film9, is taken out from the processing vessel 56, and transferred to theliquid removing rolls 62 making up the liquid removing unit 16 forremoving the redundant portion of the pre-flux liquid 9 a. That is, theprinted wiring board 1, carrying the pre-flux liquid 9 a, is passedthrough the sponge-like liquid removing rolls 62 so as to be therebyfreed of the unneeded portion of the pre-flux liquid 9 a. The lowerliquid removing roll 62 below the printed wiring board 1 is partiallyhidden in the lower saucer 63 in which is circulated the pre-flux liquid9 a. So, the fresh pre-flux liquid 9 a is circulated at all times in thelower saucer 63 to prevent the liquid component immersing the liquidremoving roll 62 from being oxidized to cause peeling of the pre-fluxfilm 9. The printed wiring board 1, freed of the surface pre-flux liquid9 a, is transferred to a transporting unit 71 of the water washing unit66 from the liquid removing rolls 62 also operating as transportingmeans.

The printed wiring board 1, freed of the surface pre-flux liquid 9 a bythe liquid removing unit 16, is freed at step S13 of the redundantportion of the pre-flux liquid 9 a affixed to its surface by the waterwashing unit 66. Specifically, as the printed wiring board 1 istransferred by the transporting unit 71 at a transfer rate e.g., of 3m/min, it is sprayed with new water at ambient temperature, that is newfresh water, under a spraying pressure not less than 0.1 MPa, by eachthree spraying units 71 provided on the the upper and lower sides of theprinted wiring board 1. This rinses the pre-flux liquid off from theprinted wiring board 1. By using fresh water for water washing in thisstep, the pre-flux liquid 9 a is prevented from being transferred to thenext step. The printed wiring board 1, washed with water by the waterwashing unit 66, is transported from the transporting unit 71 to thetransporting unit 74 of the water washing unit 67.

The printed wiring board 1, washed with water at step S14 by the waterwashing unit 66, is freed of excess pre-flux liquid 9 a, affixed to itssurface, by the water washing unit 67. Specifically, as the printedwiring board 1 is transferred by the transporting unit 74 at a transferrate e.g., of 3 m/min, it is sprayed with new water at ambienttemperature, that is new fresh water, under a spraying pressure not lessthan 0.1 MPa, by each two spraying units 71 provided on the the upperand lower sides of the printed wiring board 1. This completely rinsesthe pre-flux liquid off from the printed wiring board 1. By using freshwater for water washing in this step, the pre-flux liquid 9 a isprevented from being transferred to the next step. The printed wiringboard 1, washed with water by the water washing unit 66, is transportedfrom the transporting unit 74 to the transporting unit 77 of the airblower unit 68.

The printed wiring board 1, now carrying the pre-flux film 9, is washedwith water in two stages by the water washing units 66, 67, whereby theexcess pre-flux liquid 9 a affixed to its surface can be removedpositively. By using fresh water as rinsing water at the time ofremoving the excess pre-flux liquid 9 a attached to the printed wiringboard 1 at steps S12 and S13, the pre-flux liquid 9 a may be preventedfrom being transferred to the next step.

The printed wiring board 1, washed with new water by the water washingunit 67, is freed of the moisture affixed to its surface by the airblower unit 68. Specifically, as the printed wiring board 1 istransferred by the transporting unit 77 at a transfer rate e.g., of 3m/min, air is ejected by the air blowers 78 onto the upper and lowersides of the printed wiring board 1 to remove the moisture positivelyfrom the upper and lower sides of the printed wiring board 1.

The printed wiring board 1, freed of the excess moisture by the airblower unit 68, is dried at step S16 by the drier unit 18. That is, asthe printed wiring board 1 is transferred by the transporting unit 84 ata transfer rate e.g., of 3 m/min, it is cooled at ambient temperaturefor approximately 20 seconds at ambient temperature.

At step S17, the printed wiring board 1 from the drying unit 18 iscooled by a cooling unit 19. That is, the present printed wiring board 1is transferred by the transporting mechanism 84 at a transfer rate e.g.,of 3 m/min and cooled at ambient temperature for approximately 20seconds.

In the above-described surface-processing method and apparatus 10 forforming the water-soluble pre-flux film 9 on the lands 5 b, 6 b, thelands 5 b, 6 b are soft-etched by the etching unit 12 at step S2 andsubstantially acid-washed by the acid washing unit 28, by way ofperforming two-stage oxide removing step, whereby the oxides may bepositively removed and the lands 5 b, 6 b are processed to a planarsurface, as shown in FIG. 6. By the four stages of water washing atsteps S5 to S8 under different conditions employing the water washingunit 29, intermediate pressure water washing unit 30, abundant waterwashing unit 31 and the second water washing unit 32, the sulfuratedwater left on the surface of the printed wiring board 1, especially inthe via-hole 7, may be removed positively.

So, with the printed wiring board 1, it is possible to prevent the lands5 b, 6 b, planarized by soft etching at step S2 and acid washing at stepS4, from being oxidized and being again roughed in its surface by thesulfurated water left on the lands 5 b, 6 b. Moreover, with the printedwiring board 1, it is possible to prevent the plating layer 7 a in thevia-hole 7 from being oxidized and ruptured. By forming the pre-fluxfilm 9 on the lands 5 b, 6 b, processed to planar surfaces, as shown inFIG. 6, it is possible to form the pre-flux film 9 having improvedadhesion to the lands 5 b, 6 b, while it is possible to planarize thesurface of the pre-flux film 9 to improve its solder wettability.

Although the foregoing description is made of a multi-layered printedwiring board, having the lands 5 b, 6 b formed on its upper and lowersides, the present invention may also be applied to the forming of thepre-flux film 9 on a land of a printed wiring board carrying anelectrically conductive layer on only one surface thereof.

What is claimed is:
 1. A surface-processing apparatus for a multilayer printed wiring board comprising: means for etching the surface of a conductor pattern formed on at least one outer layer of a printed wiring board; first rinsing means for rinsing the surface of the printed wiring board the conductor pattern of which has been etched by said etching means; air bubble removing means for removing air bubbles affixed to the surface of the printed wiring board by immersing the printed wiring board rinsed by said first rinsing means in a water-soluble pre-flux liquid in a processing vessel; pre-flux forming means for forming a pre-flux film on said conductor pattern of said outer layer of said printed wiring board in the pre-flux liquid, freed of air bubbles by said air bubble removing means, using an in-liquid spray provided in said pre-flux liquid in said processing vessel; liquid removing means for removing the pre-flux liquid from the surface of said printed wiring board carrying said pre-flux film; and second rinsing means for rinsing the surface of said printed wiring board from the surface of which said pre-flux liquid has been removed by said liquid removing means.
 2. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said etching means removes the surface of said conductor pattern by 1.5 to 2.5 μm.
 3. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said first rinsing means rinses the surface of the printed wiring board, the conductor pattern of which has been etched, with acid, then rinses the acid-rinsed surface with water under a condition of not less than 0.5 MPa/cm2 and subsequently rinses the water-washed surface with water under a condition of not less than 5 lit/cm2 min.
 4. The surface-processing apparatus for a printed wiring board according to claim 3 wherein said water washing is with pure water not lower than 35 C.
 5. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said pre-flux film is mainly composed of an imidazole compound and is formed to a thickness of 0.2 to 0.3 μm on said conductor pattern.
 6. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said air bubble removing means is a sponge-like roll.
 7. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said pre-flux forming means transfers said printed wiring board using upper and lower paired rolls provided at a spacing from each other larger than the thickness of the printed wiring board.
 8. The surface-processing apparatus for a printed wiring board according to claim 1 wherein said liquid removing means includes a sponge-like roll and a lower saucer in which said pre-flux liquid is stored in circulation on said lower saucer holding said sponge like roll, such that half of said sponge like roll is immersed in said pre-flux liquid. 